Heretofore as a very small size electromagnetic actuator which utilizes semiconductor technology, there is for example, as proposed by the present inventor, the planar type mirror galvanometer (Japanese Patent Application Nos. 5-320524 and 6-9824), the planar type electromagnetic relay (Japanese Patent Application No. 5-320525), or the optical detecting instrument (Japanese Patent Application No. 6-310657).
A description of such conventional electromagnetic actuators is given below using as an example, a planar type mirror galvanometer.
Mirror galvanometers are used for example in laser scanners which deflection scan a laser beam, operating on the theory that when an electrical current is passed through a movable coil arranged in a magnetic field, an electromagnetic force is generated due to the interaction between the electrical current and the magnetic field, producing a rotational force (torque) proportional to the electrical current. The construction involves a device utilizing galvanometer theory where a movable coil rotates to an angle where the torque and a spring force are in equilibrium, the presence and size of a current being detected by an indicator needle swung by the movable coil. However instead of the indicator needle which rotates integrally with the movable coil, a reflecting mirror is provided.
Conventional practical mirror galvanometers use for example a movable piece of iron arranged in a magnetic field instead of the movable coil, with a magnetic path formed around the periphery of the movable piece of iron by means of a magnetic body including two permanent magnets and four magnetic poles. The magnetic flux between the poles is altered by changing the size and direction of a current flowing in a drive coil wound around the magnetic body, so that a reflecting mirror is swung by the movable piece of iron, to thus deflection scan a laser beam (see for example "Practical Laser Technology", Kyoritsu Publishing Company, Dec. 10, 1987, p210-212).
With the conventional mirror galvanometer however, miniaturization is difficult due for example to the drive coil being mechanically wound. There is thus the problem that miniaturization of laser scanning systems using such mirror galvanometers, and miniaturization of laser application equipment using such systems becomes difficult.
In order to solve this problem, the present inventors proposed the beforementioned very small thin type planar mirror galvanometer.
This planar type mirror galvanometer is discussed below.
With this planar type mirror galvanometer; a silicon substrate has integrally formed therewith, a planar movable plate, and a torsion bar at a central position of the movable plate for axially supporting the movable plate so as to be swingable in a perpendicular direction relative to the silicon substrate. A planar coil for producing a magnetic field by means of an electric current, is provided on an upper face peripheral edge portion of the movable plate, and a fully reflecting mirror is provided on an upper face central portion which is surrounded by the planar coil of the movable plate. A pair of electrode terminals for electrically connecting to the planar coil via a torsion bar portion, are provided on the silicon substrate side which supports the movable plate. Moreover, permanent magnets forming pairs with each other, are secured at the periphery of the movable plate so that a static magnetic field generated thereby acts on the planar coil portions located on the opposite ends of the movable plate which is parallel with the axial direction of the torsion bars. With the abovementioned patent applications, the pairs of permanent magnets are respectively located above and below the opposite end portions of the movable plate, the construction being such that the static magnetic fields generated between the pairs of permanent magnets intersect the drive coil in predetermined directions.
Operation of such a planar type mirror galvanometer is as follows.
A magnetic field is formed by means of the permanent magnets at opposite ends of the movable plate, in a direction so as to intersect the planar coil lying along the planar face of the movable plate. When a current flows in the planar coil positioned in this magnetic field, a magnetic force acts in a direction according to Fleming's left hand rule for current, magnetic flux density, and force, on the opposite ends of the movable plate in proportion to the current density and magnetic flux density of the planar coil, so that the movable plate is rotated. At this time, the torsion bars are twisted with the rotation of the movable plate, producing a spring reaction force, so that the movable plate rotates to a position where the magnetic force and the spring reaction force are in equilibrium. Since the angle of rotation of the moveable plate is proportional to the current flowing in the planar coil, then if the current flowing in the planar coil is controlled, the rotation angle of the movable plate can be controlled.
Consequently, the direction of reflection of a laser beam incident on a fully reflecting mirror in a plane perpendicular to the axis of the torsion bar, can be freely controlled. Hence if the displacement angle of the fully reflecting mirror is continuously cycled back and forth, then laser beam scanning can be effected.
Moreover there is also a two axis mirror galvanometer provided with a frame like outer movable plate axially supported on a silicon substrate by means of first torsion bars, and a planar inner movable plate axially supported on the outer movable plate by means of second torsion bars aligned perpendicular to the first torsion bars, and having a fully reflecting mirror on an upper central surface of the inner movable plate.
This two axis construction has the advantage that if a current is passed through both a planar coil on the upper face of the outer movable plate, and a planar coil on the upper face of the inner movable plate, then the outer movable plate and the inner movable plate rotate in directions which are perpendicular to each other. Hence if a laser beam is deflection scanned by the fully reflecting mirror, then two dimensional scanning can be carried out.
In the case where a current is only passed through one of the planar coils, the movement is the same as for the single axis construction.
With such planar type mirror galvanometers, in the case of both the single axis and the two axis arrangements, wiring for connecting the planar coil provided on the upper face of the movable plate to electrode terminals on the silicon substrate side which supports the movable plate, has heretofore been patterned on the torsion bar portion.
There is thus the likelihood of disconnection of the metal material of the planar coil due to metal fatigue resulting from the back and forth twisting movement of the torsion bar when the movable plate is being driven. Hence there is the problem that the life of the mirror galvanometer is limited by the fatigue strength of the planar coil.
The present invention takes into consideration the above situation with the object of providing an electromagnetic actuator and a method of manufacture therefor, which eliminates the occurrence of drive coil disconnection faults.